Image projection apparatus and illumination optical system

ABSTRACT

An image projection apparatus includes: an illumination optical system; a projection optical system assembled integrally with the illumination optical system; and a frame fixed to only one system, that has a larger weight, of the illumination optical system and the projection optical system.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/277,252, filed Sep. 27, 2016, which is acontinuation application of U.S. patent application Ser. No. 14/158,169,filed Jan. 17, 2014, and claims the benefit of priority from priorJapanese Patent Application JP 2013-15894, filed Jan. 30, 2013, theentire content of which is hereby incorporated by reference.

BACKGROUND

The present disclosure relates to an illumination optical system and animage projection apparatus including the illumination optical system anda projection optical system.

A projector (image projection apparatus) has been known in the past,which includes an illumination optical system (illuminating unit) with alight source configured of a halogen lamp, a metal halide lamp, etc.,and a projection optical system (projection unit) including an opticalmodulator, a projection lens, etc. (see Japanese Unexamined PatentApplication Publication No. 2011-2611).

In recent years, a small (palm-sized) and lightweight portable projectorknown as a microprojector is beginning to be widely used in such aprojector field. In such a microprojector, a light emitting diode (LED)is mainly used as a light source of an illuminating unit. Furthermore,recently, a laser has been noticed in light of expansion of a colorreproduction range and reduction in power consumption.

SUMMARY

Such a microprojector including an LED or a laser as a light source isextremely small in size and weight compared with a projector including alamp as a light source. On the other hand, in a short-focus-typemicroprojector, a projection optical system is often configured of acombination of a lens and a concave or convex mirror, which particularlymakes it difficult to adjust size and weight of the projection opticalsystem to be similar to size and weight of an illumination opticalsystem. It is to be noted that the short focus type generally refers toa type where the projection optical system has a throw ratio of, forexample, 0.75 or less. In particular, a microprojector having the throwratio of, for example, 0.38 or less may be referred to as of anultra-short focus type. Herein, the throw ratio is a value obtained bydividing a distance from an emitting section of the projection opticalsystem to a screen surface by a width of a projection screen. A smallerthrow ratio indicates that a relatively large screen is projectable at ashorter distance. Since such difficulty exists, in the case where eachof the illumination optical system and the projection optical system isfixed to a frame (or housing) for containing such systems, the frame maybe desirable to be structurally reinforced as by sufficiently increasingthe thickness of the frame. As a result, the overall configuration ofthe microprojector is difficult to be reduced in size and be decreasedin weight. In addition, light axis misalignment may occur between theillumination optical system and the projection optical system due toexpansion and construction of the frame caused by temperature variation,deflection of the frame caused by weight of the illumination opticalsystem and the projection optical system, or deformation thereof causedby shock, thereby leading to degradation in display performance.

It is desirable to provide an image projection apparatus capable ofexhibiting excellent display performance despite a more-compactconfiguration thereof, and an illumination optical system to be used inthe image projection apparatus.

According to an embodiment of the present disclosure, there is providedan image projection apparatus, including: an illumination opticalsystem; a projection optical system assembled integrally with theillumination optical system; and a frame fixed to only one system, thathas a larger weight, of the illumination optical system and theprojection optical system.

According to an embodiment of the present disclosure, there is providedan illumination optical system configured to be mounted on an imageprojection apparatus including a projection optical system and a frame,the illumination optical system being assembled integrally with theprojection optical system. Further, only one system, that has a largerweight, of the illumination optical system and the projection opticalsystem is fixed to the frame.

In the illumination optical system and the image projection apparatusaccording to the above-described respective embodiments of the presentdisclosure, the illumination optical system and the projection opticalsystem are assembled integrally; hence, the image projection apparatushas a compact configuration compared with a case where the illuminationoptical system and the projection optical system are individually fixedto the frame. In addition, only one system, that has a larger weight, ofthe illumination optical system and the projection optical system isfixed to the frame; hence, light axis misalignment due to variation inor distortion (deflection) of a dimension of the frame is less likely tooccur between the illumination optical system and the projection opticalsystem.

According to the illumination optical system and the image projectionapparatus of the above-described respective embodiments of the presentdisclosure, light axis misalignment due to variation in or distortion(deflection) of the dimension of the frame is prevented despite amore-compact configuration. Therefore, excellent display performance isexhibited.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments and,together with the specification, serve to explain the principles of thetechnology.

FIG. 1 is a schematic diagram illustrating an exemplary overallconfiguration of a projector according to an embodiment of the presentdisclosure.

FIG. 2A is an exploded perspective diagram illustrating a relevant partof the projector illustrated in FIG. 1 in an exploded manner.

FIG. 2B is a perspective diagram illustrating the relevant part of theprojector illustrated in FIG. 1.

FIG. 3A is an exploded perspective diagram illustrating a modificationof the relevant part of the projector illustrated in FIG. 1 in anexploded manner (Modification 1).

FIG. 3B is a perspective diagram illustrating the modification of therelevant part of the projector illustrated in FIG. 1 (Modification 1).

DETAILED DESCRIPTION

Some existing microprojectors adopt a module structure, which includesan illumination optical system and a projection optical system assembledintegrally, from a viewpoint of housing within a portable apparatus.Such a module structure includes an illumination optical system thatuses a light emitting diode (LED), a laser, or the like as a lightsource for size reduction, and includes a normal-focus-type projectionoptical system having a relatively-small dimension and arelatively-large throw ratio, for example, larger than 0.75. In apossible desktop projector, the illumination optical system, which usesthe LED, the laser, or the like as the light source for size reduction,is combined with a large, short-focus-type projection optical systemhaving a relatively-small throw ratio. In the case of such a desktopprojector, when the illumination optical system is provided as a commonillumination optical system module having a reduced size, and such anillumination optical system module is combined with a smallnormal-focus-type projection optical system, it is possible to achieve aprojector that is allowed to be housed within a portable apparatus.Furthermore, when the common illumination optical system module having areduced size is combined with a large short-focus-type projectionoptical system, it is possible to advantageously configure ashort-focus-type desktop projector.

Moreover, in the existing projectors, the illumination optical systemand the projection optical system are individually assembled on the sameblock (frame). However, the illumination optical system and theprojection optical system may be preferably assembled integrally inlight of preventing light axis misalignment between the illuminationoptical system and the projection optical system. Furthermore, when theillumination optical system and the projection optical system are eachfixed onto the frame after being assembled into one unit, the frame maybe deformed at the time of the fixation of the illumination opticalsystem and the projection optical system onto the frame depending onflatness, dimension accuracy, strength, etc. of the frame, whichdisadvantageously leads to light axis misalignment. Hence, only one ofthe illumination optical system and the projection optical system may bedesirably fixed to the frame.

However, in the case where the projection optical system is fixed to thecommon illumination optical system as described above, a weight ratiobetween the two systems may be an issue. For example, while weight of asmall projection optical system may be one third or less of weight of anillumination optical system, weight of a large projection optical systemmay be three times or more as large as the weight of the illuminationoptical system. Here, if a system having a smaller weight is fixed tothe frame, the system having the smaller weight is easily deformed dueto the weight of the other system having a larger weight. In addition,when the frame receives a shock, influence of the shock is larger.Consequently, only the system having the larger weight may be preferablyfixed to the frame.

Hereinafter, an embodiment of the present disclosure is described indetail with reference to accompanying drawings.

[General Configuration of Projector]

FIG. 1 illustrates an overall configuration of a projector according toan embodiment of the present disclosure. This projector (imageprojection apparatus) projects an image (image light) to a screen 30(surface for projection), and includes an illuminating unit 1, aprojection optical system 2 that is configured to perform image displayusing illuminating light from the illuminating unit 1, and a frame 3 asan outer package containing the illumination unit 1 and the projectionoptical system 2. The throw ratio of the projection optical system 2 maybe, for example, 0.75 or smaller. The image projection apparatus havingsuch a throw ratio is referred to as of a short focus type. If the throwratio of the projection optical system 2 is particularly small and maybe, for example, 0.38 or smaller, such an image projection apparatus maybe referred to as of an ultra-short focus type. The illuminating unit 1and the projection optical system 2 are assembled integrally, and, forexample, only the projection optical system 2 may be fixed to the frame3. The frame 3 may be part of an outer package.

(Illuminating Unit 1)

The illuminating unit 1 includes, within a housing 10, a red laser 11R,a green laser 11G, a blue laser 11B, coupling lenses 12R, 12G, and 12B,dichroic prisms 131 and 132, a fly-eye lens 14, and a condenser lens 15.In the drawing, Z0 indicates a light axis.

The red laser 11R, the green laser 11G, and the blue laser 11B are threetypes of laser light sources that emit red laser light, green laserlight, and blue laser light, respectively. Such laser light sourcesconfigure a light source section. For example, the red laser 11R, thegreen laser 11G, and the blue laser 11B may each emit pulse light.Specifically, for example, each laser may intermittently emit laserlight at a predetermined light emission frequency (in a predeterminedlight emission cycle). For example, the red laser 11R, the green laser11G, and the blue laser 11B may each be configured of a semiconductorlaser, a solid-state laser, or the like. In the case where each laser isconfigured of a semiconductor laser, for example, the red laser lightmay have a wavelength λr of about 600 nm to 700 nm both inclusive, thegreen laser light may have a wavelength λg of about 500 nm to 600 nmboth inclusive, and the blue laser light may have a wavelength λb ofabout 400 nm to 500 nm both inclusive.

The coupling lens 12G is a lens (coupling lens) that collimates thegreen laser light emitted from the green laser 11G, and allows thecollimated light (i.e., converts the green laser light into parallellight, and allows the parallel light) to be coupled with the dichroicprism 131. Similarly, the coupling lens 12B is a lens (coupling lens)that collimates the blue laser light emitted from the blue laser 11B,and allows the collimated light to be coupled with the dichroic prism131. The coupling lens 12R is a lens (coupling lens) that collimates thered laser light emitted from the red laser 11R, and allows thecollimated light to be coupled with the dichroic prism 132. It is to benoted that although each of the coupling lenses 12R, 12G, and 12Bcollimates the entering laser light (converts the entering laser lightinto parallel light) in this case, this is not limitative. The laserlight may not be collimated (converted into parallel light) by thecoupling lenses 12R, 12G, and 12B. However, the laser light may bedesirably collimated as described above since a unit configuration isallowed to be reduced in size thereby.

The dichroic prism 131 is a prism that selectively transmits the bluelaser light entering through the coupling lens 12B, while selectivelyreflecting the green laser light entering through the coupling lens 12G.The dichroic prism 132 is a prism that selectively transmits the bluelaser light and the green laser light emitted from the dichroic prism131, while selectively reflecting the red laser light entering throughthe coupling lens 12R. Consequently, color composition (optical pathcomposition) is performed on the red laser light, the green laser light,and the blue laser light.

The fly-eye lens 14 is an optical component (integrator) including aplurality of lenses (unit cells) that are two-dimensionally arranged ona substrate, and is configured to spatially divide an incident beam intobeams corresponding to such arranged lenses, and emit the divided beams.The fly-eye lens 14 is here disposed on an optical path between thedichroic prism 132 and the condenser lens 17. The fly-eye lens 14 emitsthe divided beams in a superimposed manner. This achieves homogenizationof light emitted from the fly-eye lens 14 (homogenization of lightamount distribution in a plane). In the fly-eye lens 14, in order toefficiently utilize also obliquely-incident light as illuminating light,the unit cells (unit lenses each having a predetermined curvature) maybe preferably formed not only on a light incident side but also on alight emitting side of the fly-eye lens 14.

The condenser lens 15 condenses light emitted from the fly-eye lens 14,and emits the condensed light as illuminating light.

The illuminating unit 1 further includes a reflective liquid crystalpanel 16 as an optical modulator and a polarization beam splitter (PBS)17.

The PBS 17 is an optical component that selectively transmits aparticular type of polarized light (for example, p-polarized light),while selectively reflecting another type of polarized light (forexample, s-polarized light). Consequently, the illuminating light (forexample, s-polarized light) from the illuminating unit 1 is selectivelyreflected and enters the reflective liquid crystal panel 16, and imagelight (for example, p-polarized light) emitted from the reflectiveliquid crystal panel 16 is selectively transmitted and enters aprojection lens 21 described later.

It is to be noted that an undepicted field lens may be disposed on anoptical path between the PBS 17 and the reflective liquid crystal panel16. The field lens allows the illuminating light to telecentricallyenter the reflective liquid crystal panel 16, and thereby theilluminating unit 1 is allowed to be compactified.

The reflective liquid crystal panel 16 is an optical modulator thatreflects the illuminating light from the illuminating unit 1 whilemodulating the illuminating light based on an image signal supplied froman undepicted display control section, and thus emits image light. Inthis operation, the reflective liquid crystal panel 16 reflects theilluminating light such that a type of polarized light at lightincidence is different from a type of polarized light at light emission.For example, such a reflective liquid crystal panel 16 may be configuredof a liquid crystal device such as liquid crystal on silicon (LCOS).

(Projection Optical System 2)

For example, the projection optical system 2 may include a lens barrel22 containing one or more projection lenses 21. The projection lens 21is a lens that (expansively) projects the illuminating light (imagelight) modulated by the reflective liquid crystal panel 16 onto thescreen 30.

In the case of a short-focus-type projection optical system 2, forexample, a concave or convex mirror may be disposed, which reflectslight emitted from the one or more projection lenses 21, and projectsthe light onto the screen 30. This allows a large image plane to beprojected onto the screen 30 even when a distance from the projectionoptical system 2 to the screen 30 is short.

[Assembling Example of Illuminating Unit 1 and Projection Optical System2]

A detailed positional layout of a relevant part of the projector of thisembodiment is now described with reference to FIGS. 2A and 2B. FIG. 2Ais an exploded perspective diagram of the relevant part of the projectorof this embodiment while the relevant part is exploded into componentsof the illuminating unit 1, the projection optical system 2, and theframe 3. FIG. 2B is a perspective diagram illustrating an assembledstate of the components. In the projector of this embodiment, forexample, the illuminating unit 1 and the projection optical system 2 maybe fixed to each other while their respective surfaces extending along alight axis Z0 are opposed to each other. In this projector, theprojection optical system 2 has a weight larger than that of theilluminating unit 1. The weight of the projection optical system 2 ispreferably three times or more as large as the weight of theilluminating unit 1. Hence, the illuminating unit 1 is fixed to theprojection optical system 2, and only the projection optical system 2 isfixed to the frame 3. The illuminating unit 1 and the frame 3 areprovided to be away from each other without direct contact. On the otherhand, the illuminating unit 1 and the projection optical system 2 arefixed to each other in a direct contact manner. The housing 10 of theilluminating unit 1 is attached to the projection optical system 2.

For example, the lens barrel 22 may have cylindrical portions 22A to 22Cdisposed in order along the light axis Z0. For example, the cylindricalportions 22A to 22C may hold one or a plurality of lenses. Thecylindrical portions 22A to 22C may also hold a concave or convex mirrorthat reflects light emitted from the one or the plurality of lenses. Thecylindrical portions 22A to 22C may further hold a plane mirror thatreflects light emitted from the concave or convex mirror. For example,two flanges 23 may be provided at different places on the bottom (aportion to be contacted with the frame 3) of the cylindrical portion22A. In FIGS. 2A and 2B, one of the flanges 23 is located behind thecylindrical portions 22A and 22B, and is therefore not viewable. Eachflange 23 has a fitting hole 41B and two screw-clamping holes 43. Forexample, a plate-like connection section 24 extending along the lightaxis Z0 may be provided alongside of the cylindrical portion 22B on anend face 22BS of the cylindrical portion 22B on a side opposite to thecylindrical portion 22A. The connection section 24 has bosses 51A and51B and two threaded holes 53 on its top face 24S that extends along thelight axis Z0. The top face 24S is a surface that is to abut on a bottomface 10S, which also extends along the light axis Z0, of the housing 10.Here, “along the light axis Z0” means that a relative angle to the lightaxis Z0 is 0° to 45° both inclusive. It is to be noted that each of thetop face 24S and the bottom face 10S may be desirably parallel to thelight axis Z0. Such a parallel arrangement facilitates formation of thetop face 24S and the bottom face 10S, and facilitates fixing operationof the lens barrel 22 to the housing 10. In such a case, each of the topface 24S and the bottom face 10S does not limitedly exist on the lightaxis Z0. Although the lens barrel 22 has the cylindrical portions 22A to22C in the above description, the configuration of the lens barrel 22 isnot limited thereto. The lens barrel 22 may have another configurationas long as the lens barrel 22 holds one or a plurality of lenses. Morepreferably, the lens barrel 22 may hold a concave, convex, or planemirror in addition to the one or the plurality of lenses.

The housing 10 has an opening 10W as a passage of light that is emittedfrom the PBS 17 to the outside. The illuminating unit 1 is fixed to thelens barrel 22 such that the opening 10W of the housing 10 is opposed toan end face of the cylindrical portion 22C of the lens barrel 22 of theprojection optical system 2, and the light axis Z0 is aligned. Thehousing 10 has fitting holes 52A and 52B and two screw-clamping holes54. The fitting holes 52A and 52B are fitted with the bosses 51A and 51Bprovided on the connection section 24. Consequently, relative positionsbetween the housing 10 and the lens barrel 22 are determined. Therespective two screw-clamping holes 54 run through the housing 10, andare provided at positions corresponding to the two threaded holes 53provided in the connection section 24 so as to communicate with thethreaded holes 53. Screws 55 are inserted into the threaded holes 53 andthe screw-clamping holes 54 communicating with each other, so that thelens barrel 22 (projection optical system 2) is fastened to theilluminating unit 1. It is to be noted that the relative positionsbetween the illuminating unit 1 and the projection optical system 2 maybe adjusted along the light axis Z0. For example, this may allowadjustment of relative positions between the reflective liquid crystalpanel 16 of the illuminating unit 1 and the projection lens 21 of theprojection optical system 2. Such adjustment of the relative positionsmay be performed by a helicoid adjustment mechanism that is configuredto move the cylindrical portion 22B or 22C of the lens barrel 22 backand forth along the light axis by means of a helical groove in the lensbarrel. Alternatively, such adjustment may be performed by a slidemechanism that is configured to slide the housing 10 with respect to thelens barrel 22. Alternatively, gutter may be provided in an attachingsection of the housing 10 so that the relative position of the housing10 to the lens barrel 22 is adjustable by a jig before fixation. It isto be noted that the relative position may be adjusted not only by themethod described above but also by another method. For example, thehousing 10 may be preferably configured of a material having excellentheat conductivity such as metal. Furthermore, the housing 10 may moredesirably have a structure having excellent radiation performance, forexample, by providing a radiation fin so that heat is not easilyconducted from the light source to the lens barrel 22.

For example, the frame 3 may be formed of ABS resin. The frame 3 has twobosses 41A and four threaded holes 42 on its top face 3S. Each boss 41Ais fitted in each fitting hole 41B of the flange 23. Consequently,relative positions between the frame 3 and the lens barrel 22 aredetermined. Each threaded hole 42 communicates with each screw-clampinghole 43 of the flange 23, and the lens barrel 22 (projection opticalsystem 2) is fastened to the frame 3 by screws 44 inserted into thethreaded holes 42 and the screw-clamping holes 43.

[Display Operation of Projector]

In this projector, as illustrated in FIG. 1, first, the illuminatingunit 1 operates as follows: the laser light of the respective colors(the red laser light, the green laser light, and the blue laser light)emitted from the red laser 11R, the green laser 11G, and the blue laser11B are collimated by the coupling lenses 12R, 12G, and 12B,respectively, into parallel light. Subsequently, such laser light of therespective color collimated into the parallel light is subjected tocolor composition (optical path composition) by the dichroic prisms 131and 132. The laser light of the respective colors subjected to theoptical path composition passes through the fly-eye lens 14 and thecondenser lens 15 in this order so as to be formed into illuminatinglight, and then enters the PBS 17. In this operation, the fly-eye lens14 homogenizes the light entering the PBS 17 (homogenizes light amountdistribution in a plane).

The illuminating light entering the PBS 17 is selectively reflected bythe PBS 17, and enters the reflective liquid crystal panel 16. Thereflective liquid crystal panel 16 reflects the illuminating light whilemodulating the illuminating light based on an image signal, and thusemits the modulated light as image light. In this operation, since atype of polarized light at light incidence is different from a type ofpolarized light at light emission, the image light emitted from thereflective liquid crystal panel 16 is selectively transmitted by the PBS17, and enters the projection optical system 2. The image light enteringthe projection optical system 2 is (expansively) projected onto thescreen 30 by the projection lens 21, etc.

At this time, for example, each of the red laser 11R, the green laser11G, and the blue laser 11B may perform intermittent light emissionoperation at a predetermined light emission frequency. As a result, thelaser light of the respective colors (red laser light, green laserlight, and blue laser light) is sequentially emitted in atime-divisional manner. In the reflective liquid crystal panel 16, thelaser light of the respective colors is sequentially modulated in atime-divisional manner based on image signals of the respective colorcomponents (a red color component, a green color component, and a bluecolor component) corresponding thereto. In this way, this projectorperforms color image display based on the image signals.

[Functions and Effects of Projector]

In this way, in this embodiment, the projection optical system 2, whichhas a relatively-large weight between the illuminating unit 1 and theprojection optical system 2 fixed to each other, is fixed to the frame3. On the other hand, the illuminating unit 1 having a relatively-smallweight is fixed to the projection optical system 2 instead of beingfixed to the frame 3. As a result, the projector of this embodiment hasa compact configuration compared with a case where the illuminating unit1 and the projection optical system 2 are individually fixed to theframe 3. In addition, such a configuration suppresses occurrence ofpositional misalignment between the light axis of the illuminating unit1 and the light axis of the projection optical system 2 due to variationin or distortion (deflection) of a dimension of the frame 3 associatedwith heat or weight. In the case where the weight of the illuminatingunit 1 is one third or less of the weight of the projection opticalsystem 2, the projection optical system 2 fixed to the frame 3 is lesslikely to receive an excessive load even upon receiving shock byfalling, etc., and the position misalignment between the light axis ofthe illuminating unit 1 and the light axis of the projection opticalsystem 2 is also less likely to occur. Consequently, this projectorexhibits excellent display performance. It is to be noted that theilluminating unit 1 and the frame 3 may be connected to each other by acomponent having no fixation function of the mutual positionalrelationship, such as a flexible wiring board or a flexible radiationcomponent.

In this embodiment, in particular, the bottom face 10S of theilluminating unit 1 and the top face 24S of the projection opticalsystem 2 each extend along the light axis Z0, and are fixed to eachother in an abutting manner. Consequently, area of each of the bottomface 10S and the top face 24S fixed to each other in an abutting manneris sufficiently secured without being limited by a bore of the lensbarrel 22 (diameter of a projection lens). Consequently, theilluminating unit 1 and the projection optical system 2 are structurallystably held. As a result, the projector exhibits more excellent displayperformance.

Furthermore, in the projector of this embodiment, the illuminating unit1 is not contacted with the frame 3, and is provided to be away from theframe 3. As a result, a space that serves as an air flow path for heatradiation to the surrounding of the illuminating unit 1 is easilysecured, and thereby it is possible to sufficiently cool theilluminating unit 1 during operation. Consequently, even if thisprojector as a whole is reduced in size, heating of the frame 3 issufficiently suppressed, and thus reliability in safety is alsoimproved.

Furthermore, the illuminating unit 1 of the projector of this embodimentis formed as one unit in such a manner that the laser light sources, theoptical multiplexers (dichroic prisms 131 and 132), the reflectiveliquid crystal panel 16, and the PBS 17 are contained in one housing 10.This unit configuration allows the overall configuration of theprojector to be compactified, and is suitable for improvement inefficiency of assembling operation and improvement in accuracy.

[Modification 1]

FIGS. 3A and 3B each illustrate a relevant part of a projector as amodification (Modification 1) of this embodiment. FIG. 3A is an explodedperspective diagram illustrating the relevant part of the projector asModification 1 while the relevant part is exploded into components of anilluminating unit 1A, a projection optical system 2A, and the frame 3.FIG. 3B is a perspective diagram illustrating an assembled state of thecomponents.

In the projector of the above-described embodiment, the illuminatingunit 1 and the projection optical system 2 are fixed to each other whilethe bottom face 10S and the top face 24S, which each extend along thelight axis Z0, are opposed to each other. On the other hand, theprojector of Modification 1 includes the illuminating unit 1A and theprojection optical system 2A. The illuminating unit 1A and theprojection optical system 2A are fixed to each other while respectivesurfaces thereof, i.e., an end face 10BS and an end face 22BS (describedlater) each extending in a direction intersecting with the light axisZ0, are opposed to each other. Here, “direction intersecting with thelight axis Z0” means that a relative angle to the light axis Z0 islarger than 45° and equal to or smaller than 90°. It is to be noted thatboth the end face 10BS and the end face 22BS may be desirably orthogonalto the light axis Z0. Such an orthogonal arrangement facilitatesformation of the end face 10BS and the end face 22BS, and facilitatesfixing operation of the illuminating unit 1A (a housing 10A and aconnection component 10B) to the lens barrel 22.

In the illuminating unit 1A, an annular connection component 10B havinga cylindrical opening 10K is fixed to the housing 10A. The housing 10Amay have a configuration substantially similar to the configuration ofthe housing 10 except for having the connection component 10B, forexample. The opening 10K is provided at a position corresponding to anemitting position of image light that is emitted from the reflectiveliquid crystal panel 16 and is then selectively transmitted by the PBS17. As described above, the end face 10BS of the connection component10B on a side opposite to the housing 10A is fixed to the end face 22BSin an abutting manner. Specifically, for example, the end face 22BS mayhave two bosses 61 and two screw-clamping holes 63, while the end face10BS has two fitting holes 62 and two threaded holes 64 that run throughthe connection component 10B. Each boss 61 fits in each fitting hole 62,so that relative positions between the illuminating unit 1A and theprojection optical system 2A are determined. The two screw-clampingholes 63 communicate with the two threaded holes 64, respectively, andthe projection optical system 2A is fastened to the illuminating unit 1Aby screws 65 inserted into the screw-clamping holes 63 and the threadedholes 64.

The projector including the illuminating unit 1A and the projectionoptical system 2A which are configured in the above way, also exhibitsfunctions and effects similar to those of the projector of theabove-described embodiment. In particular, such a configuration issuitable for reduction in dimension in a direction along the light axisZ0 compared with the projector of the above-described embodiment.

Although the technology of the present disclosure has been describedwith the example embodiment and the modification thereof hereinbefore,the technology of the present disclosure is not limited to theabove-described embodiment and the like, and various modifications oralterations may be made. For example, although the above-describedembodiment has been described with an exemplary case where the top face24S of the connection section 24 and the bottom face 10S of the housing10 abut on each other, the technology of the present disclosure is notlimited thereto. For example, the top face 24S of the connection section24 and the bottom face 10S of the housing 10 may be opposed to eachother with another component in between so that the connection section24 and the housing 10 are indirectly fixed to each other.

Moreover, although the above-described embodiment and Modification 1have been described with an exemplary case where the majorpolarized-light component of the illuminating light is an s-polarizedlight component, this is not limitative. Conversely, in the case wherethe major polarized-light component of the illuminating light is ap-polarized light component, the technology of the present disclosure isalso applicable.

Moreover, although the above-described embodiment and Modification 1have been described with an exemplary case where the projection opticalsystem has a weight larger than that of the illuminating unit, thetechnology of the present disclosure is not limited thereto.Specifically, the illuminating unit may have a weight larger than thatof the projection optical system. In such a case, the illuminating unitis fixed to the frame.

Furthermore, although the above-described embodiment and Modification 1have been described with an exemplary case where the plurality of (red,green, and blue) light sources are each a laser light source, this isnot limitative, and another type of light source (for example, LED,etc.) may be used. Alternatively, a laser light source and another typeof light source (for example, LED, etc.) may be used in combination.

In addition, although the above-described embodiment and Modification 1have been described with an exemplary case where the optical modulatoris a reflective liquid crystal device, this is not limitative.Specifically, for example, the optical modulator may be a transmissiveliquid crystal device, or may be an optical modulator other than theliquid crystal device (for example, a digital micro-mirror device(DMD)).

Moreover, the above-described embodiment and Modification 1 have beendescribed with an exemplary case of using three types of light sourcesemitting light having different wavelengths. However, for example, onetype of light source, two types of light sources, or four or more typesof light sources may be used instead of the three types of lightsources.

Furthermore, although the above-described embodiment and Modification 1have been described while the components (optical systems) of theilluminating unit and the projector are specifically mentioned, it isnot necessary to provide all of the mentioned components, and othercomponents may be additionally provided. Specifically, for example,dichroic mirrors may be provided in place of the dichroic prisms 131 and132.

It is possible to achieve at least the following configurations from theabove-described example embodiment and the modifications of thedisclosure.

(1) An image projection apparatus, including:

-   -   an illumination optical system;    -   a projection optical system assembled integrally with the        illumination optical system; and    -   a frame fixed to only one system, that has a larger weight, of        the illumination optical system and the projection optical        system.

(2) The image projection apparatus according to (1), wherein theprojection optical system has a weight larger than a weight of theillumination optical system.

(3) The image projection apparatus according to (2), wherein theillumination optical system includes a light source, and the lightsource is configured of one of a light emitting diode and a laser.

(4) The image projection apparatus according to (2) or (3), wherein theprojection optical system has a throw ratio of 0.75 or smaller.

(5) The image projection apparatus according to (4), wherein the weightof the projection optical system is three times or more as large as theweight of the illumination optical system.

(6) The image projection apparatus according to any one of (1) to (5),further including a housing containing the illumination optical system,wherein the housing and the projection optical system are assembledintegrally.

(7) The image projection apparatus according to (6), wherein the housingis formed of metal.

(8) The image projection apparatus according to any one of (1) to (7),wherein the frame serves as an outer package containing the illuminationoptical system and the projection optical system.

(9) The image projection apparatus according to (2), wherein theillumination optical system and the frame are provided to be away fromeach other without being in direct contact with each other.

(10) The image projection apparatus according to (3), wherein theillumination optical system further includes an optical multiplexer andan optical modulator.

(11) The image projection apparatus according to any one of (1) to (10),wherein the illumination optical system and the projection opticalsystem are fixed to each other in direct contact with each other, or areindirectly fixed to each other with another component in between.

(12) The image projection apparatus according to (10) or (11), whereinthe illumination optical system and the projection optical system arefixed to each other to allow a surface of the illumination opticalsystem and a surface of the projection optical system to be opposed toeach other, the surface of the illumination optical system and thesurface of the projection optical system each being parallel to a lightaxis.

(13) The image projection apparatus according to (10) or (11), whereinthe illumination optical system and the projection optical system arefixed to each other to allow a surface of the illumination opticalsystem and a surface of the projection optical system to be opposed toeach other, the surface of the illumination optical system and thesurface of the projection optical system each being orthogonal to alight axis.

(14) The image projection apparatus according to any one of (1) to (13),wherein respective relative positions of the illumination optical systemand the projection optical system are adjustable in a light axisdirection.

(15) An illumination optical system configured to be mounted on an imageprojection apparatus including a projection optical system and a frame,

-   -   the illumination optical system being assembled integrally with        the projection optical system, wherein    -   only one system, that has a larger weight, of the illumination        optical system and the projection optical system is fixed to the        frame.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An image projection apparatus, comprising: anillumination optical unit; a projection optical unit assembledintegrally with the illumination optical unit; and a frame fixed to onlyone unit of the illumination optical unit or the projection optical unitthat has a larger weight as compared to other.
 2. The image projectionapparatus according to claim 1, wherein the projection optical unit hasa weight larger than a weight of the illumination optical unit.
 3. Theimage projection apparatus according to claim 1, wherein theillumination optical unit includes a light source, and the light sourceis configured of one of a light emitting diode or a laser.
 4. The imageprojection apparatus according to claim 1, wherein the projectionoptical unit has a throw ratio of 0.75 or smaller.
 5. The imageprojection apparatus according to claim 2, wherein the weight of theprojection optical unit is three times or more as large as the weight ofthe illumination optical unit.
 6. The image projection apparatusaccording to claim 1, further comprising a housing containing theillumination optical unit, wherein the housing and the projectionoptical unit are assembled integrally.
 7. The image projection apparatusaccording to claim 6, wherein the housing is of metal.
 8. The imageprojection apparatus according to claim 1, wherein the frame serves asan outer package containing the illumination optical unit and theprojection optical unit.
 9. The image projection apparatus according toclaim 2, wherein the illumination optical unit and the frame are awayfrom each other without being in direct contact with each other.
 10. Theimage projection apparatus according to claim 3, wherein theillumination optical unit further includes: an optical multiplexerconfigured to selectively transmit and reflect light emitted by thelight source; and an optical modulator configured to modulate lightemitted by the light source.
 11. The image projection apparatusaccording to claim 1, wherein the illumination optical unit and theprojection optical unit are fixed to each other in direct contact witheach other, or are indirectly fixed to each other with a component inbetween.
 12. The image projection apparatus according to claim 1,wherein the illumination optical unit and the projection optical unitare fixed to each other; wherein a first surface of the illuminationoptical unit and a second surface of the projection optical unit areopposed to each other, and wherein each of the first surface of theillumination optical unit and the second surface of the projectionoptical unit is parallel to a light axis.
 13. The image projectionapparatus according to claim 1, wherein the illumination optical unitand the projection optical unit are fixed to each other, wherein a firstsurface of the illumination optical unit and a second surface of theprojection optical unit are opposed to each other, and wherein each ofthe first surface of the illumination optical unit and the secondsurface of the projection optical unit is orthogonal to a light axis.14. The image projection apparatus according to claim 1, whereinrespective relative positions of the illumination optical unit and theprojection optical unit are adjustable in a light axis direction. 15.The image projection apparatus according to claim 1, wherein theillumination optical unit is fixed to the projection optical unit, andwherein the projection optical unit is fixed to the frame.
 16. The imageprojection apparatus according to claim 1, wherein the illuminationoptical unit and the frame are in indirect contact with each otherthrough the projection optical unit.